1. Field of the Invention
The invention relates to a screen for reducing noise in buildings alongside a road where the traffic is sufficient to require such protection. This noise reducing screen comprises at least a continuous portion in the form of tunnel which is interposed between an elongated noise source such as a motor-road and a building on both sides of a perpendicular drawn from the building point the most remote from the elongated noise source and located at a predetermined distance therefrom to the elongated noise source.
2. Description of the Prior Art
It is known that the nuisance resulting from traffic noise, particularly on main roads or railways, is a serious problem, particularly in build-up areas. The noise is due partly to motor vehicles, more particularly with internal combustion motors, and partly to the noise of wheels on roads or railways.
The noise in a roadside building may be reduced by disposing continuous walls between the building and the source of noise, which is distributed all the way along the road, the walls reducing the amount of transmitted sound energy in a manner which is substantially dependent on the surface density (mass per unit surface) of the walls. In general, the continuous walls can be regarded as an "umbrella" over the building to be protected, just as if the noise source was an elongated light source.
FIGS. 1 to 3 show three examples of roads provided with conventional continuous screens for reducing noise in adjacent buildings.
In the relatively simple case of a low building on one side only of the road, the screening can be reduced to a single continuous side wall (FIG. 1). The ends of the wall are those points whose distance to the building involves such a noise attenuation that the attenuated noise can be tolerated. If the building to be protected is relatively high, the side screens cannot be made sufficiently high; in such cases, they may be supplemented by a continuous cover over part (FIG. 2) or all of a traffic artery. This cover can be overhanging or supported by posts. Finally, if relatively high buildings have to be shielded on both sides of the road, the road has to be enclosed in a true tunnel (FIG. 3).
In the two examples with cover, we have assumed that the ground does not have any relief. If the road is in a cutting and has to be covered, the cover can bear on the top of the lateral embankments and/or on the retaining walls.
Sound measurements teach that the sound energy received from a portion of a traffic artery by an observer located near this traffic artery and at a certain height above ground level varies substantially in proportion to the plane angle under which the observer is seeing the artery portion. In practice, it is desired to produce a reduction in sound energy of the order of 10 to 20 decibels (corresponding to sound ratios of the order of 10 to 100).
In very many cases, therefore, it appears desirable to screen from the observer's view nearly all the traffic artery, which is thereby converted into a true, but very long, tunnel. This results in a first difficulty in that such work is extremely expensive. In addition, it is known that existing long road tunnels pose serious ventilation problems if the internal atmospheric pollution due to exhaust gases, inter alia carbon monoxide and fumes, is to be limited to a level compatible with the health or even the survival of persons and with the safety of the traffic (e.g. by not obscuring air). Ventilation can be provided only by heavy, expensive ventilation apparatus, the investment and maintenance costs of which increase in proportion to the amount of traffic.
The object of the invention is to provide a noise-reducing system of the kind previously defined, which is at least largely free from the aforementioned disadvantages.
To this end, a noise-reducing system of the aforementioned kind according to the invention is characterized in that, in addition to a continuous screening wall, wall and cover or tunnel structure, it comprises an at least partly discontinuous screening structure, the discontinuous part being made up of sectional elements, hereinafter called sound-proofing elements, having the shape of posts, posts with an upper overhanging bracket or double posts with a cross-beam, which are disposed substantially at right angles to the road and which are staggered, allowing for their dimensions in the cross-sectional plane of the post, bracket or beam, at intervals such that an observer is screened from the road traffic at any point in the building to be protected.
The various shapes of the sound-proofing elements, simple post, jib or gantry, depend on the relief of the ground and/or the local environmental conditions at the building to be protected. The sound-proofing elements may have the form of simple beams bearing (on one or both sides) on the tops of embankments lining a cutting. They can be provided with an intermediate wall or retaining posts.
Each of the sound-proofing elements may be either:
solid, at least in certain parts thereof, in which case it has a preferably I-shaped cross-section for the horizontal parts and a rectangular cross-section for the vertical parts, the solid parts being made from a material such as reinforced or prestressed concrete, steel, a light metal or alloy, a plastic preferably reinforced with glass or nylon, or wood, preferably glued plywood; or
hollow, at least in certain parts thereof, in which case the cross-section is preferably rectangular, the hollow parts being made from a material such as steel sheet, sheets of a light metal or alloy, or glass or nylon reinforced plastics.
As a rule, owing to the fact that the sound-proofing elements are disposed at relatively large distances from the buildings to be protected and the sound energy transmitted per unit surface of the source decreases substantially in inverse proportion to the square of the distance, the requirements regarding the surface density of the sound-proofing elements can be considerably less exacting than for the surface density of continuous walls which are near the region to be protected.
Finally, according to partly known features each of the sound-proofing elements may also comprise either:
a plate or layer of absorbent material along at least one vertical side of the solid parts, such material being e.g. straw-cement, mineral wool, open-cell foam plastics or reconstituted wood felt, the layer being protected if required by a flexible plastics diaphragm; or
a perforated sheet along at least one vertical side of the hollow parts, the resulting cavity containing at least one panel of absorbent material such as straw-cement, mineral wool, open-cell plastics foam or reconstituted wood felt, the panel being protected if required, by enveloping it in a welded plastics bag.
The last-mentioned feature absorbs the fraction of sound energy which is transmitted to the region to be protected, as a result of reflection or diffusion between successive adjacent sound-proofing elements. If only one surface of each sound-proofing element is provided with absorbent material, that surface is selected which is visible to the observer to be protected. The absorbent element can be protected by a flexible plastics diaphragm or bag so as to shelter it from rain, fumes and corrosive agents of all kinds.